This invention relates to an inductor comprising a magnetic core made of flat magnetic powders and a coil wound around the magnetic core, wherein the magnetic core and the coil are integrally pressure-molded. For example, this invention is applicable to an inductor component which is used in a power supply circuit of an electronic device having a reduced size.
The miniaturization of an electronic device requires an inductor to have not only a sufficient performance but also a low-profile. For example, a low-profile inductor (i.e. a thin inductor) is disclosed or suggested in each of JP-A 2007-67214, JP-A 2008-66671, JP-A 2008-181923 and JP-A H11 (1999)-176680, contents of which are incorporated herein by reference.
The power inductor (the inductor) disclosed in JP-A 2007-67214 comprises an insulating body (a magnetic core) and a coiled conductor (a coil). The magnetic core has a plate-like shape which is thin in an upper-to-lower direction. The coil is formed within the magnetic core. The coil has a central axis extending in the upper-to-lower direction.
The magnetic substrate (the inductor) disclosed in JP-A 2008-66671 comprises a magnetic core formed from a plurality of thin sheets laminated in an upper-to-lower direction. The magnetic core has a through hole which pierces the magnetic core in the upper-to-lower direction. The magnetic substrate further comprises a plating seed layer. The plating seed layer is formed on an outer surface of the magnetic core and an inner surface of the through hole so that the magnetic substrate is formed with a coiled conductor (a coil) having a central axis extending in parallel to the outer surface of the magnetic core.
The inductor disclosed in JP-A 2008-181923 comprises a magnetic core and a coiled wire (a coil). The magnetic core is made of flat particles (flat magnetic powders). The magnetic core has an upper surface perpendicular to an upper-to-lower direction, and a through hole piercing the magnetic core in the upper-to-lower direction. The coil is wound around a part of the magnetic core so as to pass through the through hole. Accordingly, the coil has a central axis extending in parallel to the upper surface of the magnetic core.
The magnetic core disclosed in JP-A H11 (1999)-176680 is formed from a plurality of thin sheets each made of soft magnetic metal powders (flat magnetic powders). The thin sheets are pressure-molded in a state where the thin sheets are stacked in an upper-to-lower direction. The magnetic core is stamped out from the pressure-molded thin sheets so as to have a toroidal shape.
The central axis of the coil of the inductor of JP-A 2007-67214 is perpendicular to the plate-like shape of the inductor. Accordingly, the inductor is excited in the upper-to-lower direction. However, the inductor is thin in the upper-to-lower direction. It is therefore difficult to improve the effective permeability because of the influence of the diamagnetic field. In other words, it is difficult to obtain a large inductance when the inductor becomes thin.
Complicated processes are required to form the inductor of JP-A 2008-66671. Moreover, the coil of JP-A 2008-66671 is formed by an electroplating. Accordingly, the time for the plating process becomes longer as the cross-section of the coil becomes larger. It is therefore difficult to reduce a direct current resistance as compared with an inductor formed by a general winding process.
The coil of the inductor of JP-A 2008-181923 is wound around the pressure-molded magnetic core. Similarly, when an inductor is made from the magnetic core of JP-A H11 (1999)-176680, it is necessary to wind a coil around the pressure-molded magnetic core. In other words, when the inductor is made by using the magnetic core disclosed in JP-A 2008-181923 or JP-A H11 (1999)-176680, it is necessary to wind the coil after the magnetic core is completely formed. When the magnetic core has a reduced size, the coil is required to pass through the small through hole. Accordingly, it is difficult to form the inductor.